Radiocommunication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also to provide the capabilities needed to support next generation radiocommunication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radiocommunication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network. Alternatively, a radiocommunication system can evolve from one generation to the next while still providing backward compatibility for legacy equipment.
One example of such an evolved network is based upon the Universal Mobile Telephone System (UMTS) which is an existing third generation (3G) radiocommunication system that is evolving into High Speed Packet Access (HSPA) technology. Yet another alternative is the introduction of a new air interface technology within the UMTS framework, e.g., the so-called Long Term Evolution (LTE) technology. Target performance goals for LTE systems include, for example, support for 200 active calls per 5 MHz cell and sub 5 ms latency for small IP packets. Each new generation, or partial generation, of mobile communication systems add complexity and abilities to mobile communication systems and this can be expected to continue with either enhancements to proposed systems or completely new systems in the future.
Mobile networks are typically subdivided into cells, in order to re-use air interface resources (frequencies, time slots, codes) from area to area and thereby increase the total capacity. The need for capacity gain in next generation systems applies both in the uplink and downlink. Hence it is natural to define a cell as an object with both uplink and downlink transmission capabilities. An individual UE is typically served by the same cell in both up- and downlink. One exception to that rule is UTRAN using HSDPA and HSUPA. A UE can be supported by up to 6 cells simultaneously (active set for soft handover), but the HSUPA uplink may use a subset of those 6 cells. Furthermore, only one cell within the active set supports the HS-DSCH channel, i.e. the channel carrying user data. In all of these exception cases, i.e., where different cells can serve a UE on the uplink and downlink, the choice of uplink cell(s) serving a specific UE is a subset of the cell(s) serving the same UE in the downlink. The choice of uplink cells are furthermore based on downlink measurements.
The tight association between uplinks and downlinks in such systems requires planning, so that uplinks and downlinks have comparable coverage. As an example, consider that the UE selects the best cell to camp on in idle mode, based on downlink signal strength and quality. If the uplink for that UE would have less coverage, the UE may fail to establish communication, although it is mandated to stay in the best cell from a downlink perspective.
A cell is supported by Radio Base Station (RBS) equipment at a RBS site. The RBS typically has one set of uplink and downlink antennas, which are close to the RBS itself. Another deployment option is a Distributed Antenna System (DAS), where a number of smaller antennas are distributed in a building. Yet another option is “leaking cable”, where the antenna is effectively distributed over several 100 meters. Nevertheless, in the above deployment scenarios, the antennas behave as one single antenna and there is no selection of uplink antennas separated from selection of downlink antennas.
In a cellular network there will always be areas with high traffic, i.e. a high concentration of users. In those areas it would be desirable to deploy additional capacity to maintain user satisfaction with the radiocommunication service. The added capacity could, e.g., be provided in the form of an additional macro base station or by deploying nodes with lower output power and thus covering a smaller area in order to concentrate the capacity boost on a smaller area. There will also be areas with bad coverage where there is a need for coverage extension, and again one way to do that is to deploy a node with low output power to concentrate the coverage boost in a small area.
One reason for choosing nodes with lower output power in the above cases is that the impact on the macro network can be minimized, e.g. it is a smaller area where the macro network may experience interference. Currently there is a strong drive in the industry in the direction towards the use of low power nodes. The different terms used to describe this type of network deployments include heterogeneous networks, sometimes called “HetNets” or multilayer networks. FIG. 1 illustrates a macro base station 100 which provides a wide area coverage (also called macro cell 102), and also lower power nodes that are deployed to provide small area capacity/coverage within the macro cell 102. For example, pico base stations 104, relays 106 and home base stations (femto cell clusters 108) are shown in FIG. 1 as examples of lower power nodes which can supplement the coverage provided by base station 100.
When the same carrier is used for macro- and pico-cells, the small cells are inherently “unbalanced” between downlink and uplink. In the uplink the macrocell and picocell are similar in sensitivity, so the best radio link is mainly determined by path loss towards macrocell and pico cell, respectively. In the downlink the transmit power difference, e.g., 20 W and 1 W, will decrease the area where the picocell link is better. This is illustrated in the FIG. 2, where ‘RSRP border’ 200 depicts the point of ‘equal downlinks’ and ‘RSRP+offset’ 202 depicts the point where uplink path loss is equal for macrocell 204 and picocell 206. UEs (not shown) located between the RSRP border 200 and the RSRP+offset border 202 will thus have different optimal uplink and downlink. There is a need to identify if a particular UE is in this border area, in order to allocate reception resources. If the pico cell 206 and the macrocell 204 have different physical identities (e.g. cell scrambling code in UTRAN or Physical Cell Id in E-UTRAN), then the UE could send measurement reports about the cells in the vicinity.
A more generalized situation is a network consisting of several uplink antennas and several downlink antennas. The uplink and downlink antennas need not be co-located. A specific cell may be supported by N uplink antennas and M downlink antennas. One reason for not allocating one cell per antenna could be planning issues, i.e. neighbor relations between cells need to be updated too frequently. Another reason may be degraded UE battery life, i.e. moving UEs need to perform cell updates more frequently. In the above cases there is a need to identify the best uplink to use, which may be different from the downlink.
A current solution in LTE for detecting a best uplink antenna is to configure separate cells (PCI) for each antenna, so that UE can identify the different downlinks. Then the UE is configured to monitor and report DL quality (RSRP and/or RSRQ) from different cells. Using that information, path loss is derived, e.g., based on DL TX powers antenna gains, etc. The best uplink antenna associated with the UE is then estimated based on antenna gains, and that antenna is activated for this UE (meaning that UE-specific processing for that antenna is started).
However, this solution has certain drawbacks including, for example, more difficult cell planning, more UE measurements means more UE power drain and more signaling over the air interface (thereby reducing bandwidth for other signaling).
Accordingly, it would be desirable to develop other methods, devices, systems and software for selecting an uplink antenna for a UE.
ABBREVIATIONS/ACRONYMSC-RNTICell Radio Network Temporary IdentifiereNBEnhanced NodeBLTELong term evolutionMIMOMultiple-Input Multiple-OutputOFDMOrthogonal Frequency Division Multiple AccessRRMRadio Resource ManagementSIBSystem Information BlockSRSSounding Reference SignalUEUser equipmentUASLUplink Antenna Selection LogicULUplinkDLDownlinkPDCPPacket Data Convergence ProtocolPDUProtocol Data UnitRLCRadio Link ControllerMACMedia Access ControlPHYPhysicalDRXDiscontinuous Reception